Motor vehicle internal combustion engines use a throttle body to govern the engine power settings. Some engines have additional charging equipment including turbo and supercharger mechanisms that compress intake air upstream of the throttle body to enhance engine performance. All internal combustion engines must receive a constant supply of clean air in order to enable the combustion of the fuel. The engine induction system is located upstream of the engine air intake and its primary functions are air filtration and noise attenuation.
The induction system begins with an inlet duct which draws cool dry air into the system. The inlet duct will deliver the air into an air filter housing that has an internal filter to capture incoming particulates to protect the engine. The air filter housing will also typically have a mass air flow meter port and a sensor downstream of the filter, to meter the air for combustion. The outlet duct will be connected between the air filter housing and the engine air intake. The air filter housing can be mounted to the engine or on the vehicle body structure. If mounted on the body structure, the duct will need a compliant feature such as a flexible bellows to decouple normal engine motion from the body mounted air filter housing. The induction system provides a pathway to deliver filtered dry cool air to the engine.
Air induction systems must also attenuate acoustic noise that is produced from the engine. Vehicles must comply with Federal regulations limiting vehicle pass-by noise. The engine will release noise from the throttle body that has harmonic components that are orders of engine speed. It may also contain higher frequency content that is produced from high RPM components like turbos and superchargers. Inductions systems will use the air filter housing size, geometry, and high and low frequency tuners to meet defined sub-system performance noise targets.
Vehicle emission standards have been mandated by the Federal government. Some engines use a strategically placed hydrocarbon adsorber in the induction system to catch hydrocarbons that are leaking from parked engines. The hydrocarbon adsorber uses carbon or other materials to capture the hydrocarbons before they escape the induction system and enter the environment. The adsorber is typically packaged on the clean filtered side of the induction system and has some exposed surface area adjacent to incoming air flow streams. This exposure allows the hydrocarbons to be captured upon engine shutdown and then be stripped from the adsorber material when the engine is running.
Induction system pressure loss is very important to develop peak engine power. Internal air flow within a duct will add incremental restriction if the area is constricted or if the boundary condition is irregular or coarse. Studies have shown that internal air flow within the bellows region of the duct assembly develops a higher restriction than flow through a smooth tube.
The clean air duct must fit within the distance between the air filter housing and the engine air inlet. Some applications can present a very short duct length due to the close proximity of the engine inlet and air filter housing. Incorporation of a high frequency tuner will reduce the available length for the bellows. The shorter length will eliminate convolutes increasing the stress per convolute reducing the durability life of the duct. Applications with short longitudinal lengths where length is consumed by bellows and tuner limit hydrocarbon filter space. It would be desirable to provide a new and improved air duct assembly for efficiently communicating air from the air filter housing to the engine air intake in a limited packaging space.